This invention relates to the measurement of retroreflectivity, especially such measurement of a retroreflective medium. The invention is more particularly directed to a technique for measuring retroreflectivity of a reflective medium in which a laser is used to illuminate an area of the medium with a known quantity of light at a selected incidence angle, which light is reflected back and measured at a selected observation angle.
The present invention, while of general application, finds particular utility in surveys of retroreflective traffic markings on highways or roadways, especially painted stripes in which retroreflective beads of glass or other material are located on the painted surface.
Thus far, no instrumentation has been developed for measuring the performance of highway stripes and detecting bead erosion on a continuous basis, which is convenient to use at troublesome spots, such as at curves, bridge approaches, etc. Previously, bead erosion at such places was discovered primarily if a motorist happened to report heavy wear at that area. Also, because of the nature of the retroreflective particles, their reflective properties could reasonably be tested only at night or under other conditions of substantial darkness.